Revised Abstract: Gastrointestinal cancers and inflammatory bowel diseases (IBD) comprise a major health concern, creating an interest in regulatory mechanisms that mediate growth, differentiation and apoptosis in the digestive tract. ZBP-89 (ZNF148, Zfp148, BFCOL1, BERF1) is a conserved mammalian transcription factor and signaling molecule that co-regulates these processes. In one such pathway, ZBP-89 activity potentiated induction of the cyclin dependent kinase inhibitor, p21-waf1, by the short-chain fatty acid, butyrate. Activation of p21-waf1 expression, in turn, induces growth arrest and differentiation in gastrointestinal cell lines. Enhancement of the butyrate of p21-waf1 is dependent upon an amino-terminal acidic domain in ZBP-89, which also mediates interaction with the transcriptional co-activator p300. Alternative splicing in humans, but not mice, generates a truncated ZBP-89 isoform, deltaNter, which lacks the p300 interaction domain and is co-expressed with FL ZBP-89 in several gastrointestinal tissues. Since deltaNter retains a DNA-binding domain, it should act as a dominant negative antagonist of FL-ZBP-89. By targeting exon 4 of ZBP-89, a mouse model of deltaNter expression has been developed. Aim 1 of this proposal will determine the physiological consequences of heterozygous and homozygous deltaNter expression, with particular emphasis on the gastrointestinal tract. Preliminary results show that deltaNter/deltaNter mice experience growth delay and may have abnormal colonic mucosal immunity. Aim 2 is focused on determining the expression pattern of FL and deltaNter isoforms, as it occurs naturally in humans and in the mouse model. Spatial, developmental and pathological variables will be assessed. Aim 3 is focused on in vitro interactions between the FL and deltaNter splice isoforms, with emphasis on promoter regulating activity. This may allow a functional correlation between deltaNter expression patterns (Aim 2) and the physiological targets of deltaNter over-expression (Aim 1).